1. Field of the Invention
The present invention is directed to a rotational pulse generating circuit for a motor, which generates a pulse signal in the form of ripple pulse train, and whose frequency is in response to a rotation number of the motor, by receiving, for example, a signal which is superposed with a ripple whose frequency is in proportion to a rotation number (rotational speed) of the motor, and which ripple results from the presence of a brush in the DC motor.
2. Description of the Background
A circuit is widely used in various fields wherein a DC motor position control is made, or a control is performed for positioning a member which is driven by a DC motor. For example, in a vehicle, a circuit of this kind is used in a closed condition detection device for power window and sun-roof devices, as well as in a memory for a seat device which stores a seat condition of at least one of a seat-cushion, a seat-back and a headrest, to comply with a passenger profile.
For example, in the memory seat device, the motor rotation condition has to be known, and a position sensor or the like is used for detecting the rotation condition of the motor which drives the seat device. This may be done by detecting the condition of a magnet which is fixedly mounted on a rotation shaft (i.e., the armature shaft) of the motor using a sensor such as a Hall element, and the resulting pulse signal issued from the sensor is used in a controller for the position control of the motor or the member driven by the motor. See, for example, pages 5-88 and 89 in NEW CAR MANUAL: SOARER published on May 1991 by TOYOTA MOTOR CO., LTD. In this way, the controller performs position control by reading the rotational pulse signal from the Hall element, thereby making it possible to provide a rotational pulse signal in the seat position control.
However, this conventional structure requires use of a Hall element and magnet, which increases the number of parts, lowers the assembly efficiency and increases the production costs. It is therefore desired to provide method which does not require a sensor such as a Hall element to produce a rotational pulse signal whose frequency is in proportion to the rotation number of a motor, by processing a detected signal (i.e., analog signal), such as a motor current or a motor voltage, which can be easily obtained from the motor in a direct fashion.
For example, due to that fact that in a DC motor, the presence of a brush superposes a ripple, whose frequency is in proportion to the rotation number of the motor, on a motor current, processing the motor current (i.e., analog current) generates a ripple pulse train whose frequency is in proportion to the rotation number of the motor.
However, if such a method is used, any noise other than the ripple which is superposed on the motor current has to be eliminated. To this end, in view of the fact that the frequency of the ripple pulse train is in proportion to the rotation number of the motor, the electric circuit processing the signal must be capable of adjusting a cutoff frequency of a filter in response to the rotation number of the motor. To this end, the cutoff frequency of the filter may be adjusted in response to the rotation number of the motor by feeding back the generated ripple pulses. However, before the motor is turned on, such feedback is not made, so that the correctness of the cutoff frequency of the filter is not always guaranteed.
Thus, a pulse error may occur wherein the pulse train becomes lost due to an unexpected loss of the ripples when passing through the filter, or due to an increase in the number of the pulses due to the noise. In this case an indirect estimation of the rotation number of the motor can be made on the basis of the motor current and/or the motor voltage, which makes it possible to establish a control for determining the cutoff frequency of the filter when the motor is energized, on the basis of the motor current and/or motor current.
However, due to the fact that, in general, actual electric circuits vary in rating values relative to the designed rating values, the cutoff frequency may fall outside the correct value range (i.e., permissible correct value range), which causes pulse errors similar to the above. In addition, due to the fact that the aforementioned hardware variation of the electric circuit varies with temperature, temperature changes may also shift the value of the cutoff frequency from its designed value, which may result in a pulse error. The aforementioned problems have to be solved in order to realize a pulse generating device which generates a pulse signal for position control, which signal is directly derived from a motor and without using a sensor.
Therefore, a needs exists to provide a rotational pulse generating circuit for motors which is free from the aforementioned problems.
It is, therefore, a first aspect of the present invention to provide a rotational pulse signal generating circuit which comprises a filter for eliminating noise from a signal inputted thereto, which signal is superposed with a ripple whose frequency is in dependent on a rotation number of the motor, the filter having a cutoff frequency which is variable on the basis of an external signal; a pulse shaper for converting an output signal of the filter to a pulse signal whose frequency is in response to the rotation number of the motor; a clock generator for generating a clock signal on the basis of the pulse signal and a rotational condition signal of the motor, the clock signal being fed to the filter for making the cutoff frequency thereof variable; and a correction device for preliminarily oscillating the clock signal before turning on the motor, the correction means judging whether or not an initial cutoff frequency is adequate on the basis of the preliminary oscillated clock signal, the correction device correcting the initial cutoff frequency when the result of the judgment is found to be inadequate.
In accordance with the first aspect of the present invention, the filter is fed with the clock signal which is generated on the basis of the pulse signal and the motor rotation condition signal, thereby making the cutoff frequency of the filter variable, which makes it possible to generate a ripple pulse train correctly in response to a change of the motor rotation condition which results from at least one of a motor load change, motor rotation number, motor driving voltage and rotation environment. In addition, before the motor is turned on, it is checked whether or not the initial cutoff frequency is adequate on the basis of the clock signal which is preliminarily oscillated at the clock generator. If the result is negative, the initial cutoff frequency is corrected to be adequate. Thus, even if the product has non-standard characteristics, the initial cutoff frequency is corrected upon initiation of the motor. As a result, even at the stage of inputting the pulse signal to the clock generator during the initial stage of motor initiation, the cutoff frequency which is set on the basis of the motor rotation condition signal is made adequate or correct, thereby correctly generating the pulse signal even when the motor is at its initial stage of initiation.
A second aspect of the present invention provides a rotational pulse generating circuit as a limited version of the first aspect, wherein the rotational condition signal is based on a motor rotational signal and a motor driving voltage signal, in which the correction device stores a plurality of values such that one of the values is to be selected as a adequate value of the cutoff frequency depending on a motor driving voltage, the correction device finds, when the judgment is made, the adequate value depending on the motor driving voltage represented by the motor driving voltage signal which is externally inputted, and the correction device judges whether or not the initial cutoff frequency is adequate by comparing the preliminary oscillated cutoff frequency to the found adequate value. It is to be noted that the adequate value can be a range of values.
In accordance with the second aspect of the present invention, upon judgment, the adequate value is found depending on the motor driving voltage, and it is checked whether or not the initial cutoff frequency is adequate by comparing the adequate value to the cutoff frequency based on the preliminarily oscillated clock signal. Thus, the setting of the initial cutoff frequency is made adequate in consideration of the motor driving voltage. For example, when a battery is used for driving the motor, which may change the motor driving voltage, generating the pulse signal can be made correctly.
A third aspect of the present invention is to provide a rotational pulse generating circuit as a limited version of the second aspect, wherein the correction means includes an attenuator and a controller for switching an attenuance of the attenuator, the attenuator being placed at a pre-stage of an input side of the clock generator so that an attenuance of the rotational condition signal is made variable.
In accordance with the third aspect of the present invention, when the initial cutoff frequency is found to be inadequate, the attenuator, which is placed at the pre-stage of input side of the clock generator, is controlled to change the attenuance of the motor rotation condition signal, thereby adjusting or correcting the initial cutoff frequency. Using the attenuator which amends the attenuance in switching fashion makes the circuit simple.
A fourth aspect of the present invention is to provide a rotational pulse generating circuit as a limited version of any one of the first aspect, the second aspect, and the third aspect, wherein the correction device executes the judgment procedures whenever the motor is turned on.
In accordance with the fourth aspect of the present invention, the correction device executes the judgment procedure whenever the motor is turned on, which makes it possible to set the correct initial cutoff frequency whenever the motor is turned on. For example, the set initial cutoff frequency can consider the thermal changes (including the thermal character change of the rotational pulse generating circuit, per se, and/or thermal dependency of the battery voltage), thereby generating the pulse signal more correctly.
A fifth aspect of the present invention is to provide a rotational pulse generating circuit as a limited version of the first aspect, wherein the correction device executes the judgment procedure by preliminarily oscillating the clock signal at the clock generator on the basis of the motor driving voltage signal.
In accordance with the fifth aspect of the present invention, the judging is made concurrently with the preliminary oscillation whenever the motor is turned on, which makes it possible to efficiently avoid an occurrence of pulse errors.
According to the invention, a rotational pulse generating circuit for a motor comprises a filter for eliminating noise from a first signal outputted by the motor on the basis of a cutoff frequency, the first signal including a ripple whose frequency corresponds to a rotation number of the motor; a pulse shaper for converting an output signal of the filter to a pulse signal whose frequency corresponds to the rotation number of the motor, a generator for generating a clock signal on the basis of the pulse signal and the first signal, the generator outputting the clock signal to the filter so as to vary the cutoff frequency; a pre-oscillator for pre-oscillating the clock signal at the generator before the motor is energized; and a compensating device for compensating the pre-oscillated cutoff frequency to an adequate frequency when the pre-oscillated cutoff frequency is an inadequate frequency.